/*
 * Based on arch/arm/mm/mmu.c
 *
 * Copyright (C) 1995-2005 Russell King
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#define pr_fmt(fmt) "mmu: " fmt

#define HAVE_LIBFDT_ENV_TYPE
#include <seminix/libfdt.h>
#include <seminix/pgtable.h>
#include <seminix/linkage.h>
#include <seminix/init.h>
#include <seminix/memblock.h>
#include <seminix/spinlock.h>
#include <seminix/param.h>
#include <seminix/cache.h>
#include <asm/mmu_context.h>
#include <asm/kernel-pgtable.h>
#include <asm/memory.h>
#include <asm/mmu.h>
#include <asm/boot.h>
#include <asm/sections.h>

static bool __initdata rodata_full = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED);

static int __init parse_rodata(char *arg)
{
    /* permit 'full' in addition to boolean options */
    if (!arg || strcmp(arg, "full"))
        return -EINVAL;

    rodata_full = true;
    return 0;
}
early_param("rodata", parse_rodata);

#define NO_BLOCK_MAPPINGS	BIT(0)
#define NO_CONT_MAPPINGS	BIT(1)
#define NO_EXEC_MAPPINGS	BIT(2)	/* assumes FEAT_HPDS is not used */

u64 idmap_t0sz __ro_after_init = TCR_T0SZ(VA_BITS);
u64 idmap_ptrs_per_pgd = PTRS_PER_PGD;

u64 kimage_voffset __ro_after_init;

/*
 * Empty_zero_page is a special page that is used for zero-initialized data
 * and COW.
 */
unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;

static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused;
static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused;

static DEFINE_SPINLOCK(swapper_pgdir_lock);

void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
{
    pgd_t *fixmap_pgdp;

    spin_lock(&swapper_pgdir_lock);
    fixmap_pgdp = pgd_set_fixmap(__pa_symbol(pgdp));
    WRITE_ONCE(*fixmap_pgdp, pgd);
    /*
     * We need dsb(ishst) here to ensure the page-table-walker sees
     * our new entry before set_p?d() returns. The fixmap's
     * flush_tlb_kernel_range() via clear_fixmap() does this for us.
     */
    pgd_clear_fixmap();
    spin_unlock(&swapper_pgdir_lock);
}

static phys_addr_t __init early_pgtable_alloc(int shift)
{
    phys_addr_t phys;
    void *ptr;

    phys = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);

    /*
     * The FIX_{PGD,PUD,PMD} slots may be in active use, but the FIX_PTE
     * slot will be free, so we can (ab)use the FIX_PTE slot to initialise
     * any level of table.
     */
    ptr = pte_set_fixmap(phys);

    memset(ptr, 0, PAGE_SIZE);

    /*
     * Implicit barriers also ensure the zeroed page is visible to the page
     * table walker
     */
    pte_clear_fixmap();

    return phys;
}

static bool pgattr_change_is_safe(u64 old, u64 new)
{
    /*
     * The following mapping attributes may be updated in live
     * kernel mappings without the need for break-before-make.
     */
    pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;

    /* creating or taking down mappings is always safe */
    if (old == 0 || new == 0)
        return true;

    /* live contiguous mappings may not be manipulated at all */
    if ((old | new) & PTE_CONT)
        return false;

    /* Transitioning from Non-Global to Global is unsafe */
    if (old & ~new & PTE_NG)
        return false;

    /*
     * Changing the memory type between Normal and Normal-Tagged is safe
     * since Tagged is considered a permission attribute from the
     * mismatched attribute aliases perspective.
     */
    if (((old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL)) &&
        ((new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL)))
        mask |= PTE_ATTRINDX_MASK;

    return ((old ^ new) & ~mask) == 0;
}

static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
             phys_addr_t phys, pgprot_t prot)
{
    pte_t *ptep;

    ptep = pte_set_fixmap_offset(pmdp, addr);
    do {
        pte_t old_pte = READ_ONCE(*ptep);

        set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot));

        /*
         * After the PTE entry has been populated once, we
         * only allow updates to the permission attributes.
         */
        BUG_ON(!pgattr_change_is_safe(pte_val(old_pte),
                          READ_ONCE(pte_val(*ptep))));

        phys += PAGE_SIZE;
    } while (ptep++, addr += PAGE_SIZE, addr != end);

    pte_clear_fixmap();
}

static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
                unsigned long end, phys_addr_t phys,
                pgprot_t prot,
                phys_addr_t (*pgtable_alloc)(int),
                int flags)
{
    unsigned long next;
    pmd_t pmd = READ_ONCE(*pmdp);

    BUG_ON(pmd_sect(pmd));
    if (pmd_none(pmd)) {
        pmdval_t pmdval = PMD_TYPE_TABLE | PMD_TABLE_UXN;
        phys_addr_t pte_phys;

        if (flags & NO_EXEC_MAPPINGS)
            pmdval |= PMD_TABLE_PXN;
        BUG_ON(!pgtable_alloc);
        pte_phys = pgtable_alloc(PAGE_SHIFT);
        __pmd_populate(pmdp, pte_phys, pmdval);
        pmd = READ_ONCE(*pmdp);
    }
    BUG_ON(pmd_bad(pmd));

    do {
        pgprot_t __prot = prot;

        next = pte_cont_addr_end(addr, end);

        /* use a contiguous mapping if the range is suitably aligned */
        if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
            (flags & NO_CONT_MAPPINGS) == 0)
            __prot = __pgprot(pgprot_val(prot) | PTE_CONT);

        init_pte(pmdp, addr, next, phys, __prot);

        phys += next - addr;
    } while (addr = next, addr != end);
}

static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
             phys_addr_t phys, pgprot_t prot,
             phys_addr_t (*pgtable_alloc)(int), int flags)
{
    unsigned long next;
    pmd_t *pmdp;

    pmdp = pmd_set_fixmap_offset(pudp, addr);
    do {
        pmd_t old_pmd = READ_ONCE(*pmdp);

        next = pmd_addr_end(addr, end);

        /* try section mapping first */
        if (((addr | next | phys) & ~PMD_MASK) == 0 &&
            (flags & NO_BLOCK_MAPPINGS) == 0) {
            pmd_set_huge(pmdp, phys, prot);

            /*
             * After the PMD entry has been populated once, we
             * only allow updates to the permission attributes.
             */
            BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd),
                              READ_ONCE(pmd_val(*pmdp))));
        } else {
            alloc_init_cont_pte(pmdp, addr, next, phys, prot,
                        pgtable_alloc, flags);

            BUG_ON(pmd_val(old_pmd) != 0 &&
                   pmd_val(old_pmd) != READ_ONCE(pmd_val(*pmdp)));
        }
        phys += next - addr;
    } while (pmdp++, addr = next, addr != end);

    pmd_clear_fixmap();
}

static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
                unsigned long end, phys_addr_t phys,
                pgprot_t prot,
                phys_addr_t (*pgtable_alloc)(int), int flags)
{
    unsigned long next;
    pud_t pud = READ_ONCE(*pudp);

    /*
     * Check for initial section mappings in the pgd/pud.
     */
    BUG_ON(pud_sect(pud));
    if (pud_none(pud)) {
        pudval_t pudval = PUD_TYPE_TABLE | PUD_TABLE_UXN;
        phys_addr_t pmd_phys;

        if (flags & NO_EXEC_MAPPINGS)
            pudval |= PUD_TABLE_PXN;
        BUG_ON(!pgtable_alloc);
        pmd_phys = pgtable_alloc(PMD_SHIFT);
        __pud_populate(pudp, pmd_phys, pudval);
        pud = READ_ONCE(*pudp);
    }
    BUG_ON(pud_bad(pud));

    do {
        pgprot_t __prot = prot;

        next = pmd_cont_addr_end(addr, end);

        /* use a contiguous mapping if the range is suitably aligned */
        if ((((addr | next | phys) & ~CONT_PMD_MASK) == 0) &&
            (flags & NO_CONT_MAPPINGS) == 0)
            __prot = __pgprot(pgprot_val(prot) | PTE_CONT);

        init_pmd(pudp, addr, next, phys, __prot, pgtable_alloc, flags);

        phys += next - addr;
    } while (addr = next, addr != end);
}

static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
               phys_addr_t phys, pgprot_t prot,
               phys_addr_t (*pgtable_alloc)(int),
               int flags)
{
    unsigned long next;
    pud_t *pudp;
    p4d_t *p4dp = p4d_offset(pgdp, addr);
    p4d_t p4d = READ_ONCE(*p4dp);

    if (p4d_none(p4d)) {
        p4dval_t p4dval = P4D_TYPE_TABLE | P4D_TABLE_UXN;
        phys_addr_t pud_phys;

        if (flags & NO_EXEC_MAPPINGS)
            p4dval |= P4D_TABLE_PXN;
        BUG_ON(!pgtable_alloc);
        pud_phys = pgtable_alloc(PUD_SHIFT);
        __p4d_populate(p4dp, pud_phys, p4dval);
        p4d = READ_ONCE(*p4dp);
    }
    BUG_ON(p4d_bad(p4d));

    pudp = pud_set_fixmap_offset(p4dp, addr);
    do {
        pud_t old_pud = READ_ONCE(*pudp);

        next = pud_addr_end(addr, end);

        /*
         * For 4K granule only, attempt to put down a 1GB block
         */
        if (pud_sect_supported() &&
           ((addr | next | phys) & ~PUD_MASK) == 0 &&
            (flags & NO_BLOCK_MAPPINGS) == 0) {
            pud_set_huge(pudp, phys, prot);

            /*
             * After the PUD entry has been populated once, we
             * only allow updates to the permission attributes.
             */
            BUG_ON(!pgattr_change_is_safe(pud_val(old_pud),
                              READ_ONCE(pud_val(*pudp))));
        } else {
            alloc_init_cont_pmd(pudp, addr, next, phys, prot,
                        pgtable_alloc, flags);

            BUG_ON(pud_val(old_pud) != 0 &&
                   pud_val(old_pud) != READ_ONCE(pud_val(*pudp)));
        }
        phys += next - addr;
    } while (pudp++, addr = next, addr != end);

    pud_clear_fixmap();
}

static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
                 unsigned long virt, phys_addr_t size,
                 pgprot_t prot,
                 phys_addr_t (*pgtable_alloc)(int),
                 int flags)
{
    unsigned long addr, end, next;
    pgd_t *pgdp = pgd_offset_pgd(pgdir, virt);

    /*
     * If the virtual and physical address don't have the same offset
     * within a page, we cannot map the region as the caller expects.
     */
    if (WARN_ON((phys ^ virt) & ~PAGE_MASK))
        return;

    phys &= PAGE_MASK;
    addr = virt & PAGE_MASK;
    end = PAGE_ALIGN(virt + size);

    do {
        next = pgd_addr_end(addr, end);
        alloc_init_pud(pgdp, addr, next, phys, prot, pgtable_alloc,
                   flags);
        phys += next - addr;
    } while (pgdp++, addr = next, addr != end);
}

/*
 * This function can only be used to modify existing table entries,
 * without allocating new levels of table. Note that this permits the
 * creation of new section or page entries.
 */
static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
                  phys_addr_t size, pgprot_t prot)
{
    if (virt < VA_START) {
        pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
            &phys, virt);
        return;
    }
    __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
                 NO_CONT_MAPPINGS);
}

void __init vmemmap_init(phys_addr_t phys, unsigned long virt,
                      usize size)
{
    BUG_ON(!PAGE_ALIGNED(virt));
    BUG_ON(!PAGE_ALIGNED(phys));
    BUG_ON(!PAGE_ALIGNED(size));

    __create_pgd_mapping(init_mm.pgd, phys, virt, size, PAGE_KERNEL,
                            early_pgtable_alloc, 0);
}

static inline pud_t *fixmap_pud(unsigned long addr)
{
    pgd_t *pgdp = pgd_offset_k(addr);
    p4d_t *p4dp = p4d_offset(pgdp, addr);
    p4d_t p4d = READ_ONCE(*p4dp);

    BUG_ON(p4d_none(p4d) || p4d_bad(p4d));

    return pud_offset_kimg(p4dp, addr);
}

static inline pmd_t *fixmap_pmd(unsigned long addr)
{
    pud_t *pudp = fixmap_pud(addr);
    pud_t pud = READ_ONCE(*pudp);

    BUG_ON(pud_none(pud) || pud_bad(pud));

    return pmd_offset_kimg(pudp, addr);
}

static inline pte_t * fixmap_pte(unsigned long addr)
{
    return &bm_pte[pte_index(addr)];
}

/*
 * The p*d_populate functions call virt_to_phys implicitly so they can't be used
 * directly on kernel symbols (bm_p*d). This function is called too early to use
 * lm_alias so __p*d_populate functions must be used to populate with the
 * physical address from __pa_symbol.
 */
void __init early_fixmap_init(void)
{
    pgd_t *pgdp;
    p4d_t *p4dp, p4d;
    pud_t *pudp;
    pmd_t *pmdp;
    unsigned long addr = FIXADDR_START;

    pgdp = pgd_offset_k(addr);
    p4dp = p4d_offset(pgdp, addr);
    p4d = READ_ONCE(*p4dp);
    if (CONFIG_PGTABLE_LEVELS > 3 &&
        !(p4d_none(p4d) || p4d_page_paddr(p4d) == __pa_symbol(bm_pud))) {
        /*
         * We only end up here if the kernel mapping and the fixmap
         * share the top level pgd entry, which should only happen on
         * 16k/4 levels configurations.
         */
        BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
        pudp = pud_offset_kimg(p4dp, addr);
    } else {
        if (p4d_none(p4d))
            __p4d_populate(p4dp, __pa_symbol(bm_pud), P4D_TYPE_TABLE);
        pudp = fixmap_pud(addr);
    }
    if (pud_none(READ_ONCE(*pudp)))
        __pud_populate(pudp, __pa_symbol(bm_pmd), PUD_TYPE_TABLE);
    pmdp = fixmap_pmd(addr);
    __pmd_populate(pmdp, __pa_symbol(bm_pte), PMD_TYPE_TABLE);
}

/*
 * Unusually, this is also called in IRQ context (ghes_iounmap_irq) so if we
 * ever need to use IPIs for TLB broadcasting, then we're in trouble here.
 */
void __set_fixmap(enum fixed_addresses idx,
                   phys_addr_t phys, pgprot_t flags)
{
    unsigned long addr = __fix_to_virt(idx);
    pte_t *ptep;

    BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);

    ptep = fixmap_pte(addr);

    if (pgprot_val(flags)) {
        set_pte(ptep, pfn_pte(phys >> PAGE_SHIFT, flags));
    } else {
        pte_clear(addr, ptep);
        flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
    }
}

static void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
{
    const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
    int offset;
    void *dt_virt;

    /*
     * Check whether the physical FDT address is set and meets the minimum
     * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
     * at least 8 bytes so that we can always access the magic and size
     * fields of the FDT header after mapping the first chunk, double check
     * here if that is indeed the case.
     */
    BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
    if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
        return NULL;

    /*
     * Make sure that the FDT region can be mapped without the need to
     * allocate additional translation table pages, so that it is safe
     * to call create_mapping_noalloc() this early.
     *
     * On 64k pages, the FDT will be mapped using PTEs, so we need to
     * be in the same PMD as the rest of the fixmap.
     * On 4k pages, we'll use section mappings for the FDT so we only
     * have to be in the same PUD.
     */
    BUILD_BUG_ON(dt_virt_base % SZ_2M);

    offset = dt_phys % SWAPPER_BLOCK_SIZE;
    dt_virt = (void *)dt_virt_base + offset;

    /* map the first chunk so we can read the size from the header */
    create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE),
            dt_virt_base, SWAPPER_BLOCK_SIZE, prot);

    if (fdt_magic(dt_virt) != FDT_MAGIC)
        return NULL;

    *size = fdt_totalsize(dt_virt);
    if (*size > MAX_FDT_SIZE)
        return NULL;

    if (offset + *size > (int)SWAPPER_BLOCK_SIZE)
        create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
                   round_up(offset + *size, SWAPPER_BLOCK_SIZE), prot);

    return dt_virt;
}

void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
{
    void *dt_virt;
    int size;

    dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
    if (!dt_virt)
        return NULL;

    memblock_reserve(dt_phys, size);
    return dt_virt;
}

void *__fixmap_remap_phys(u64 raw_virt, phys_addr_t phys, usize size,
    pgprot_t prot, phys_addr_t (*pgtable_alloc)(int))
{
    int offset;
    void *virt;

    BUG_ON(raw_virt < VA_START);

    if (!phys || phys % sizeof(long) || size % PAGE_SIZE)
        return NULL;

    offset = phys % PAGE_SIZE;
    virt = (void *)raw_virt + offset;

    if (!pgtable_alloc) {
        /* map the first chunk so we can read the size from the header */
        create_mapping_noalloc(round_down(phys, PAGE_SIZE),
                raw_virt, size, prot);
    } else
        __create_pgd_mapping(init_mm.pgd, round_down(phys, PAGE_SIZE),
            raw_virt, size, prot, pgtable_alloc, NO_CONT_MAPPINGS);

    return virt;
}

void *__init __fixmap_remap_console(phys_addr_t con_phys, pgprot_t prot)
{
    u64 virt = __fix_to_virt(FIX_CONSOLE_MEM_BASE);

    BUILD_BUG_ON(virt % PAGE_SIZE);

    return __fixmap_remap_phys(virt, con_phys, PAGE_SIZE, prot, NULL);
}

void *__init __fixmap_remap_spintable(phys_addr_t release_addr, pgprot_t prot)
{
    u64 virt = __fix_to_virt(FIX_SPINTABLE_BASE);

    BUILD_BUG_ON(virt % PAGE_SIZE);

    return __fixmap_remap_phys(virt, release_addr, PAGE_SIZE, prot, NULL);
}

static void __init map_kernel_segment(pgd_t *pgdp, void *va_start, void *va_end,
                      pgprot_t prot, int flags)
{
    phys_addr_t pa_start = __pa_symbol(va_start);
    unsigned long size = va_end - va_start;

    BUG_ON(!PAGE_ALIGNED(pa_start));
    BUG_ON(!PAGE_ALIGNED(size));

    __create_pgd_mapping(pgdp, pa_start, (unsigned long)va_start, size, prot,
                 early_pgtable_alloc, flags);
}

/*
 * Create fine-grained mappings for the kernel.
 */
static void __init map_kernel(pgd_t *pgdp)
{
    /*
     * External debuggers may need to write directly to the text
     * mapping to install SW breakpoints. Allow this (only) when
     * explicitly requested with rodata=off.
     */
    pgprot_t text_prot = PAGE_KERNEL_ROX;

    /*
     * Only rodata will be remapped with different permissions later on,
     * all other segments are allowed to use contiguous mappings.
     */
    map_kernel_segment(pgdp, _text, _etext, text_prot, 0);
    map_kernel_segment(pgdp, __start_rodata, __inittext_begin, PAGE_KERNEL, NO_CONT_MAPPINGS);
    map_kernel_segment(pgdp, __inittext_begin, __inittext_end, text_prot, 0);
    map_kernel_segment(pgdp, __initdata_begin, __initdata_end, PAGE_KERNEL, 0);
    map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, 0);

    if (!READ_ONCE(pgd_val(*pgd_offset_pgd(pgdp, FIXADDR_START)))) {
        /*
         * The fixmap falls in a separate pgd to the kernel, and doesn't
         * live in the carveout for the swapper_pg_dir. We can simply
         * re-use the existing dir for the fixmap.
         */
        set_pgd(pgd_offset_pgd(pgdp, FIXADDR_START),
            READ_ONCE(*pgd_offset_k(FIXADDR_START)));
    } else if (CONFIG_PGTABLE_LEVELS > 3) {
        pgd_t *bm_pgdp;
        p4d_t *bm_p4dp;
        pud_t *bm_pudp __maybe_unused;
        /*
         * The fixmap shares its top level pgd entry with the kernel
         * mapping. This can really only occur when we are running
         * with 16k/4 levels, so we can simply reuse the pud level
         * entry instead.
         */
        BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
        bm_pgdp = pgd_offset_pgd(pgdp, FIXADDR_START);
        bm_p4dp = p4d_offset(bm_pgdp, FIXADDR_START);
        bm_pudp = pud_set_fixmap_offset(bm_p4dp, FIXADDR_START);
        pud_populate(&init_mm, bm_pudp, lm_alias(bm_pmd));
        pud_clear_fixmap();
    } else {
        BUG();
    }
}

static void __init __map_memblock(pgd_t *pgdp, phys_addr_t start,
                  phys_addr_t end, pgprot_t prot, int flags)
{
    __create_pgd_mapping(pgdp, start, __phys_to_virt(start), end - start,
                 prot, early_pgtable_alloc, flags);
}

static void __init map_mem(pgd_t *pgdp)
{
    phys_addr_t kernel_start = __pa_symbol(_text);
    phys_addr_t kernel_end = __pa_symbol(__init_begin);
    struct memblock_region *reg;
    int flags = NO_EXEC_MAPPINGS;

    if (rodata_full)
        flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

    /*
     * Take care not to create a writable alias for the
     * read-only text and rodata sections of the kernel image.
     * So temporarily mark them as NOMAP to skip mappings in
     * the following for-loop
     */
    memblock_mark_nomap(kernel_start, kernel_end - kernel_start);

    /* map all the memory banks */
    for_each_memblock(memory, reg) {
        phys_addr_t start = reg->base;
        phys_addr_t end = start + reg->size;

        if (start >= end)
            break;
        if (memblock_is_nomap(reg))
            continue;

        __map_memblock(pgdp, start, end, PAGE_KERNEL, flags);
    }

    /*
     * Map the linear alias of the [_text, __init_begin) interval
     * as non-executable now, and remove the write permission in
     * mark_linear_text_alias_ro() below (which will be called after
     * alternative patching has completed). This makes the contents
     * of the region accessible to subsystems such as hibernate,
     * but protects it from inadvertent modification or execution.
     * Note that contiguous mappings cannot be remapped in this way,
     * so we should avoid them here.
     */
    __map_memblock(pgdp, kernel_start, kernel_end,
               PAGE_KERNEL, NO_CONT_MAPPINGS);
    memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
}

/*
 * paging_init() sets up the page tables, initialises the zone memory
 * maps and sets up the zero page.
 */
void __init paging_init(void)
{
    pgd_t *pgdp = pgd_set_fixmap(__pa_symbol(swapper_pg_dir));

    map_kernel(pgdp);
    map_mem(pgdp);

    pgd_clear_fixmap();

    cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
    init_mm.pgd = swapper_pg_dir;

    memblock_free(__pa_symbol(init_pg_dir),
              __pa_symbol(init_pg_end) - __pa_symbol(init_pg_dir));

    memblock_allow_resize();
}

__diag_push()
__diag_ignore_all("-Wsign-compare", "");

/*
 * Check whether a kernel address is valid (derived from arch/x86/).
 */
int kern_addr_valid(unsigned long addr)
{
    pgd_t *pgdp;
    p4d_t *p4dp;
    pud_t *pudp, pud;
    pmd_t *pmdp, pmd;
    pte_t *ptep, pte;

    if ((((long)addr) >> VA_BITS) != -1UL)
        return 0;

    pgdp = pgd_offset_k(addr);
    if (pgd_none(READ_ONCE(*pgdp)))
        return 0;

    p4dp = p4d_offset(pgdp, addr);
    if (p4d_none(READ_ONCE(*p4dp)))
        return 0;

    pudp = pud_offset(p4dp, addr);
    pud = READ_ONCE(*pudp);
    if (pud_none(pud))
        return 0;

    if (pud_sect(pud))
        return pfn_valid(pud_pfn(pud));

    pmdp = pmd_offset(pudp, addr);
    pmd = READ_ONCE(*pmdp);
    if (pmd_none(pmd))
        return 0;

    if (pmd_sect(pmd))
        return pfn_valid(pmd_pfn(pmd));

    ptep = pte_offset_kernel(pmdp, addr);
    pte = READ_ONCE(*ptep);
    if (pte_none(pte))
        return 0;

    return pfn_valid(pte_pfn(pte));
}

__diag_pop();

static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
                phys_addr_t size, pgprot_t prot)
{
    if (virt < VA_START) {
        pr_warn("BUG: not updating mapping for %pa at 0x%016lx - outside kernel range\n",
            &phys, virt);
        return;
    }

    __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
                 NO_CONT_MAPPINGS);

    /* flush the TLBs after updating live kernel mappings */
    flush_tlb_kernel_range(virt, virt + size);
}

void __init mark_linear_text_alias_ro(void)
{
    /*
     * Remove the write permissions from the linear alias of .text/.rodata
     */
    update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text),
                (unsigned long)__init_begin - (unsigned long)_text,
                PAGE_KERNEL_RO);
}

void mark_rodata_ro(void)
{
    unsigned long section_size;

    /*
     * mark .rodata as read only. Use __init_begin rather than __end_rodata
     * to cover NOTES and EXCEPTION_TABLE.
     */
    section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata;
    update_mapping_prot(__pa_symbol(__start_rodata), (unsigned long)__start_rodata,
                section_size, PAGE_KERNEL_RO);
}

int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
{
    pud_t new_pud = pfn_pud(__phys_to_pfn(phys), mk_pud_sect_prot(prot));

    BUG_ON(phys & ~PUD_MASK);
    set_pud(pudp, new_pud);
    return 1;
}

int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot)
{
    pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), mk_pmd_sect_prot(prot));

    BUG_ON(phys & ~PMD_MASK);
    set_pmd(pmdp, new_pmd);
    return 1;
}

int pud_clear_huge(pud_t *pudp)
{
    if (!pud_sect(READ_ONCE(*pudp)))
        return 0;
    pud_clear(pudp);
    return 1;
}

int pmd_clear_huge(pmd_t *pmdp)
{
    if (!pmd_sect(READ_ONCE(*pmdp)))
        return 0;
    pmd_clear(pmdp);
    return 1;
}

int pmd_free_pte_page(struct vm_area_struct *vma, pmd_t *pmdp, unsigned long addr)
{
    pte_t *table;
    pmd_t pmd;

    pmd = READ_ONCE(*pmdp);

    if (!pmd_table(pmd))
        return 1;

    table = pte_offset_kernel(pmdp, addr);
    pmd_clear(pmdp);
    flush_pmd_tlb_range(vma, addr, addr + PMD_SIZE);
    pte_free(vma->vm_mm, virt_to_page(table));
    return 0;
}

int pud_free_pmd_page(struct vm_area_struct *vma, pud_t *pudp, unsigned long addr)
{
    pmd_t *table;
    pmd_t *pmdp;
    pud_t pud;
    unsigned long next, end;

    pud = READ_ONCE(*pudp);

    if (!pud_table(pud)) {
        WARN_ON(1);
        return 1;
    }

    table = pmd_offset(pudp, addr);
    pmdp = table;
    next = addr;
    end = addr + PUD_SIZE;
    do {
        pmd_free_pte_page(vma, pmdp, next);
    } while (pmdp++, next += PMD_SIZE, next != end);

    pud_clear(pudp);
    flush_pud_tlb_range(vma, addr, end);
    pmd_free(NULL, table);
    return 1;
}

int pmd_huge(pmd_t pmd)
{
    return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
}

int pud_huge(pud_t pud)
{
#ifndef __PAGETABLE_PMD_FOLDED
    return pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT);
#else
    return 0;
#endif
}
